1. Field
Disclosed is a method for producing a diamond electrode comprising synthetically produced and electrically conductive (doped) diamond particles which are embedded in a support layer. Also disclosed is a diamond electrode comprising synthetically produced and electrically conductive (doped) diamond particles which are embedded in a support layer.
2. Related Art
Diamond electrodes are distinguished by a high overload for oxygen and hydrogen and are therefore suited for a plurality of oxidation processes in aqueous solution. Possible and particularly interesting applications lie in the field of water treatment by anodic oxidation and in the field of synthesis chemistry.
It is known to produce diamond electrodes by a direct generation of boron-doped diamond layers on substrate materials, in particular by CVD (Chemical Vapor Deposition) methods, for example in accordance with DE 10324558. From EP 1527212 a method for the production of diamond electrodes is known, in which doped, electrically conductive and synthetically produced diamond particles are embedded superficially into a metal or a metal alloy such that a conductive connection results between the metal or the metal alloy and the diamond particles. The diamond particles are mixed with powders of metals or metal alloys, which are capable of forming a non-conducting oxide layer, and are then pressed so that a pressed piece, if necessary with a support plate, is produced, which contains the diamond particles embedded in one or more layers. Low-melting materials, for example magnesium or a magnesium alloy, are proposed as starting materials for the embedding layer, which materials are melted onto a preferably metallic support layer with a higher melting point.
With regard to the prior art, reference is also made to WO 2005116298, which is concerned with the production of plastic diamond electrodes, to JP 2005272908, from which a bipolar diamond electrode is known, and to US 2005200260, which relates to a method in which metal is deposited on diamonds.
Diamond electrodes produced by the CVD method are limited with regard to their size. Larger electrode surfaces tend to the formation of cracks owing to the different coefficients of thermal expansion, which as a further consequence can lead through gas development under the diamond layer to the destruction of the electrode. Therefore, in order to guarantee the durability of the electrode, the diamond layer must have a certain minimum thickness which can only be achieved by a deposition process lasting several hours. The production costs are therefore comparatively high in the case of diamond electrodes which are produced in such a way.
Diamond electrodes produced according to EP 1527212 by the binding of diamond particles to self-passivating metals have a good durability in those media in which the metal oxide is stable under anodic or cathodic conditions. In aqueous solutions with a high halide content, and in organic solutions such as are used in electro-organic synthesis, the durability of such electrodes is somewhat less. In alternating current applications, hydride corrosion impairs the durability of the electrodes.